This is a minor visual problem; clicking the link properly produces a permission error, but it says 'Edit'
|mediawiki/extensions/Newsletter : master||Restricted Newsletter editing to "newsletter-manage" group.|
Good catch. As a general principle, users should be presented labels / links according to their permissions, in order to avoid false expectations.
If a user cannot edit a newsletter, the label should be either "View source"+ link.
This bug still exists, but was made impossible to test by the change of newsletter-create to sysop. The link still displays edit for a user with the newsletter-create right but not the newsletter-manage right, who cannot edit newsletters.